1. Field of the Invention
This invention relates to power supplies and more particularly relates to low cost, efficient, power supplies that provide alternating current (“AC”) redundancy.
2. Description of the Related Art
A power supply, sometimes known as a power supply unit or PSU, is a device or system that supplies electrical or other types of energy to an output load or group of loads. A power supply, in some embodiments may be configured to convert power in one form to another form, such as converting AC power to direct current (“DC”) power. The regulation of power supplies is typically done by incorporating circuitry to tightly control the output voltage and/or current of the power supply to a specific value. The specific value is closely maintained despite variations in the load presented to the power supply's output, or any reasonable voltage variation at the power supply's input.
For example, in an electronic device such as a computer, the power supply is typically designed to convert an AC voltage input such as is traditionally provided by a conventional wall socket, into several low-voltage DC power outputs for transmission to the internal components of the electronic device. Conversion is typically performed in stages such as a rectification stage, a pre-regulation stage such as an active harmonic filter, a regulator/chopper stage, etc. The stages may be a boost stage, a buck stage, or other derivative topology.
In some instances, redundancy of power supplies is desired to protect electronic devices from unexpected power failures. For example, two or more power supplies may be used to provide redundant DC power outputs so that in the event one power supply fails, a second or third power supply will continue to provide the necessary DC power. This is referred to as DC redundancy.
In addition to DC redundancy, some power supplies are also configured to provide AC redundancy, meaning that they receive AC input power from two or more power sources. As depicted in FIG. 1, some conventional systems require complete redundancy of two or more power supplies to provide AC redundancy. The system 100 depicts a first power supply 102 and a second power supply 104. The first power supply 102 receives an AC power waveform AC1 as an input and the second power supply 104 receives a second AC power waveform AC2 as an input. The outputs of the two power supplies 102, 104 are combined to form a redundant DC output Vout. Thus, if the AC power waveform AC1 provided to the first power supply 102 fails for some reason, the second power supply 104 continues to receive AC power from the second AC power waveform AC2, thereby providing AC redundancy protection.
In some embodiments, the first power supply 102 and the second power supply 104 may be provided in a single housing. For example, a single housing unit may include more than one AC input connector for receiving the AC power waveforms AC1, AC2. Within the single housing, the redundant power supplies 102 and 104 may be provided to receive the redundant AC power waveforms AC1, AC2 and provide an output signal Vout. However, such implementations are relatively expensive because of the cost of providing two completely redundant power supplies 102, 104.
Furthermore, another problem arises if two AC power waveforms are simultaneously applied to the input of the same power supply 102. In such a case, the two AC power waveforms may be out of phase, which can result in an overall higher voltage applied to the power supply 102. This can result a significant decrease in efficiency.